Different Radio Access Technologies (RAT:s) are available in the modern world of mobile communication, allowing a user of a user device such as a mobile terminal (User Equipment (UE)) to access communication services like voice calls, Internet browsing, video calls, file transmissions, audio/video streaming, electronic messaging and e-commerce. Radio Access Technologies can be divided into different categories.
A first and probably most widely spread category includes RATs suitable for use in mobile or cellular telecommunications systems like GSM (Global System for Mobile Communications), UMTS (Universal Mobile Telecommunications System), FOMA (Freedom of Mobile Multimedia Access), EPS (Evolved Packet System), D-AMPS (Digital-Advanced Mobile Phone Service), CDMA2000 (Code Division Multiple Access 2000) or WiMAX (Worldwide Interoperability for Microwave Access). Common examples of RATs in this first category are 3GPP (3rd Generation Partnership Project) GPRS/EDGE (General Packet Radio Service/Enhanced Data rates for Global Evolution), 3GPP WCDMA/HSPA (Wideband Code Division Multiple Access/High-Speed Packet Access), 3GPP LTE/E-UTRAN (Long-Term Evolution/Evolved Universal Terrestrial Radio Access Network), and TD-SCDMA (Time Division Synchronous Code Division Multiple Access).
A second category includes RATs which are suitable for use in short-range wireless communication networks, such as Wi-Fi or WLAN (Wireless Local Area Network). One example of a RAT in this second category is the IEEE 802.11 family of wireless standards. Other examples include Bluetooth and NFC (Near-Field Communication).
Most user devices are nowadays enabled for use with more than one RAT, such as one or more RATs selected from the first category, as well as one or more RATs selected from the second category. A mobile terminal, from now on referred to as User Equipment or UE, enabled both for cellular access (e.g. 3GPP LTE/E-UTRAN and/or WCDMA/HSPA for use in EPS and/or UMTS) and for Wi-Fi access, will be used herein as an example of such a multi-RAT-enabled user device.
Because of the inherent differences in architecture and operation between mobile telecommunications networks on the one hand and Wi-Fi networks on the other hand, in many existing setups there has not been any integration between the two. Allowing two such networks to co-exist in parallel but “hidden” from each other is fully acceptable, but not optimal from resource utilization, load distribution and user experience perspectives. Therefore, certain integration attempts have been made, as will now be described in some greater detail, however only for background purposes.
Introduction
Operators of mobile telecommunications networks are today mainly using Wi-Fi to offload traffic from the mobile networks, but the opportunity to improve end-user experience regarding performance is also becoming more important. The current Wi-Fi deployments are mainly totally separate from mobile networks, and are to be seen as non-integrated. The usage of Wi-Fi is mainly driven due to the free and wide unlicensed spectrum, and the increased availability of Wi-Fi in mobile terminals like smartphones and tablets. The end-users are also becoming more and more at ease with using Wi-Fi for example at offices and homes.
The different business segments for Wi-Fi regarding integration possibilities can be divided into mobile operator hosted/controlled versus third-party hosted/-controlled Wi-Fi APs (Access Points). Here, “third-party” is seen as anything else than a mobile operator, and that the third-party is not totally “trusted” by the mobile operator. A third-party could be for example a Wi-Fi operator or an end-user himself/herself. In both segments there exist public/hotspot, enterprise and residential deployments.
Different Types of Wi-Fi Integration to Mobile Networks
Wi-Fi integration towards the mobile core network is emerging as a good way to improve the end-user experience further. These solutions consist mainly of the following components: common authentication between 3GPP and Wi-Fi, and integration of Wi-Fi user plane traffic to the mobile core network. The common authentication is based on automatic (U)SIM-based ((Universal) Subscriber Identity Module) authentication in both access types. The Wi-Fi user plane integration gives the mobile operator an opportunity to provide the same services, like parental control and subscription-based payment methods, for the end-users both when connected via 3GPP and when connected via Wi-Fi. Different solutions are standardized in 3GPP. Overlay solutions (S2b, S2c) have been specified since 3GPP Release 8, while integration solutions (S2a) are currently work-in-progress (S2a, S2b, S2c indicating the 3GPP interface/reference point names towards the PDN-GW). These solutions are specified in 3GPP TS 23.402 (current version=11.3.0), which can be obtained from the website of the 3rd Generation Partnership Project at http://www.3gpp.com/.
Wi-Fi integration into radio access network (RAN) is also emerging as an interesting study object. This has basically two different possible levels that could be implemented either separately or together. A first level of integration is to combine both 3GPP and Wi-Fi in the small pico base stations to gain access to the Wi-Fi sites with 3GPP technology, and vice versa. A second level of integration is to integrate the Wi-Fi access tighter into the RAN by introducing enhanced network controlled traffic steering between 3GPP and Wi-Fi based on knowledge about the total situation on the different accesses. The driver for this second level of integration could be to avoid potential issues with UE (User Equipment) controlled Wi-Fi selection, such as selecting Wi-Fi when the Wi-Fi connection is bad or when the UE is moving, thus giving better end-user performance and better utilization of the combined Wi-Fi and cellular radio network resources.
FIG. 1 illustrates an existing network architecture for integration of a mobile telecommunications system 110 in the form of an EPS system, and a Wi-Fi access network 120. As is well known, EPS was introduced in 3GPP Release 8 and Release 9. For detailed information about EPS, reference is made to 3GPP TS 23.401 (current version=11.2.0). The mobile telecommunications (EPS) system 110 comprises a radio access network 112 known as E-UTRAN (Evolved Universal Terrestrial Radio Access Network) and a core network 114 known as EPC (Evolved Packet Core). The E-UTRAN has a combined base station and radio network controller known as eNodeB. The EPC has units known as MME (Mobility Management Entity) and a Serving GW (Gateway). As is seen in FIG. 1, the eNodeB is connected via the S1 interfaces, S1-MME and S1-U to the MME and Serving GW, respectively. FIG. 1 also shows how the Wi-Fi access network 120 is connected to the PDN-GW via the S2a interface and to the 3GPP AAA Server via the STa interface. The shown Wi-Fi access network is just an example deployment and contains a Wi-Fi Access Point (AP), a Wi-Fi Access Controller (AC) and a Broadband Network Gateway (BNG).
Background to Hotspot 2.0
Different standards organizations have started to recognize the needs for an enhanced user experience for Wi-Fi access, this process being driven by 3GPP operators. An example of this is the Wi-Fi Alliance with the Hotspot 2.0 (HS2.0) initiative, now officially called PassPoint. For detailed information about Hotspot 2.0, reference is made to Wi-Fi Alliance Hotspot 2.0 (Release 1) TS Version 1.0.0, which can be obtained from the website of the Wi-Fi Alliance at http://www.wi-fi.org/. HS2.0 is primarily geared towards Wi-Fi networks. HS2.0 builds on IEEE 802.11u, and adds requirements on authentication mechanisms and auto-provisioning support. For detailed information about IEEE 802.11u, reference is made to IEEE 802.11u-2011, Amendment 9: Interworking with External Networks, which can be obtained from the website http://standards.ieee.org.
The momentum of Hotspot 2.0 is due to its roaming support, its mandatory security requirements and for the level of control it provides over the terminal for network discovery and selection. Even if the current release of HS2.0 is not geared towards 3GPP interworking, 3GPP operators are trying to introduce additional traffic steering capabilities, leveraging HS2.0 802.11u mechanisms. Because of the high interest of 3GPP operators, there will be a second release of HS2.0 focusing on 3GPP interworking requirements.
The HS2.0 contains the following procedures:
1 Discovery: Where the terminal discovers a Wi-Fi network, and probes it for HS2.0 support, using 802.11u and HS 2.0 extensions.
2 Registration is performed by the terminal towards the Wi-Fi Hot-spot network if there is no valid subscription for that network.
3 Provisioning: Policy related to the created account is pushed towards the terminal. This only takes place when a registration takes place.
4 Access: Cover the requirements and procedures to associate with a HS2.0 Wi-Fi network.
Background to Access Network Discovery and Selection Function
The Access Network Discovery and Selection Function (ANDFS) is an entity defined by 3GPP for providing access discovery information as well as mobility and routing policies to the UE. The information and policies provided by the ANDSF may be subscriber specific.
Access Discovery Information is used to provide access discovery information to the UE, which can assist the UE to discover available (3GPP and) non-3GPP access networks without the burden of continuous background scanning.
Inter-System Mobility Policies (ISMP) are policies which guide the UE to select the most preferable 3GPP or non-3GPP access. The ISMP are used for UEs that access a single access (3GPP or Wi-Fi) at a time,
Inter-System Routing Policies (ISRP) are policies which guide the UE to select over which access a certain type of traffic or a certain APN shall be routed. The ISRP are used for UEs that access both 3GPP and Wi-Fi simultaneously.
Background to Permanent UE Identifiers
The different permanent UE identifiers are defined in 3GPP TS 23.003 (current version=11.2.0). The definition of International Mobile Subscriber Identity (IMSI) is shown in FIG. 2. As seen in this drawing, IMSI is composed of three parts:
1. A Mobile Country Code (MCC) consisting of three digits. The MCC uniquely identifies the country of the mobile subscriber/subscription of the UE.
2. A Mobile Network Code (MNC) consisting of two or three digits. The MNC identifies the home PLMN (Public Land Mobile Network) of the mobile subscriber/subscription. The length of the MNC (two or three digits) depends on the value of the MCC.
3. Mobile Subscriber Identification Number (MSIN) identifying the mobile subscriber within a PLMN.
The National Mobile Subscriber Identity (NMSI) consists of the Mobile Network Code (MNC) and the Mobile Subscriber Identification Number (MSIN).
The International Mobile station Equipment Identity and Software Version number (IMEISV), the International Mobile station Equipment Identity (IMEI) and the MS international PSTN/ISDN number (MSISDN) are also defined in 3GPP TS 23.003 but are not further described herein.
In the EPS (110, FIG. 1), the permanent UE identities are only known in the EPC 114, whereas the E-UTRAN 112 is only aware of temporary UE identities. An example of this is the Globally Unique Temporary UE Identity (GUTI) that uniquely identifies the MME which allocated the GUTI and also identifies the UE within the MME that allocated the GUTI. Another example used for paging purposes is the S-TMSI. GUTI and S-TMSI are also defined in the aforementioned 3GPP TS 23.003. The GUTI is allocated to the UE during an Attach procedure as defined in the afore-mentioned 3GPP TS 23.401 (also see FIGS. 3A and 3B), and the serving MME holds the association between the GUTI and the UE permanent identifier(s).
When the UE accesses a Wi-Fi network, it can be authenticated using EAP-SIM (Extensible Authentication Protocol-SIM) and EAP-AKA (Extensible Authentication Protocol-Authentication and Key Agreement) protocols. In these cases, the UE can be identified by either the full authentication Network Access Identifier (NAI) or by the fast re-authentication NAI. The full authentication NAI contains the IMSI of the UE, and the fast re-authentication NAI is similar to the temporary identities used in LTE access in the sense that it is the 3GPP AAA Server that knows the relation between the fast re-authentication NAI and the full authentication NAI.
Overview 3GPP Attach Procedure
FIGS. 3A and 3B shows an overview of the attach procedure used in for instance the E-UTRAN 112 of FIG. 1. The attach procedure is described in detail in 3GPP TS 23.401. During this attach procedure, the UE is authenticated to the network in a step 5a, using credentials stored on the (U)SIM ((Universal) Subscriber Identity Module) in the UE. At initial attach, the UE will use the IMSI as an identifier of the UE subscription (and (U)SIM). During the attach to the network, the UE might be assigned other shorter temporary identifiers such as S-TMSI, P-TMSI, URNTI, etc. The MME/SGSN in the 3GPP Core Network (CN) will be aware of the IMSI associated and the mapping to temporary identifiers when the UE has an active context in the network.
Overview of Wi-Fi Attach Procedure with EAP-SIM/AKA Authentication
FIG. 4 shows an example procedure for a Wi-Fi-enabled UE connecting to a Wi-Fi network, such as access network 120 in FIG. 1, with a Wi-Fi Access Controller (AC). Other procedures may also be used depending on implementation in the UE and network. The EAP signalling is in this procedure used to authenticate the UE towards the network. The UE uses IMSI or some other certificate to identify itself towards the network.
Some Problems with Existing Solutions
The current methods for integration of Wi-Fi into a 3GPP network described above do not offer good support for network-controlled Wi-Fi/3GPP access selection and service mapping, taking into consideration radio access related input parameters such as UE mobility, 3GPP/Wi-Fi cell and network load, radio link performance, etc.
In order to achieve this functionality, it is required to link (connect, associate) the UE context in the 3GPP radio access network (RAN)—which holds information about radio performance, UE mobility, etc. on the 3GPP side—with the UE context in the Wi-Fi network. This can then enable a network entity to take decisions whether the UE should access the Wi-Fi network or not, depending on if the UE is stationary, and/or has a good connection to the Wi-Fi AP (Access Point), etc. The decision can then be signaled to the UE or executed internally in the 3GPP/Wi-Fi network (for instance to control UE admission to Wi-Fi).
Although mechanisms have been introduced for allowing the UE to perform authentication towards the Wi-Fi network using (U)SIM credentials and identities (IMSI), there is currently no mechanism available for connecting the UE RAN context in the 3GPP RAN with the UE Wi-Fi access context.
This means that with existing solutions, there is no node in the access network that can identify a single UE to be the same UE when it is active in Wi-Fi and 3GPP, respectively—even if it is handled by the same physical base station (e.g. eNodeB, WiFi AC).